Products > Hover Fly > FAQ

Order your ready to fly Hoverfly helicopter here

Q. How do I fit the training undercarriage?
(This provides a wide base to help beginners take off and land easily without toppling over.)

A. Assemble the two tubes into a cross by pushing one through the centre hole in the other. Place it on the floor and stand the Hoverfly on it. Now tape the skids down onto the cross with short narrow strips of adhesive tape (excess from the decorative stripes supplied is ideal). Slight innaccuracy of the position of the cross will not affect flight. (See picture, right, and page 9 of the manual.)

Q. Why did my Hoverfly blast off uncontrollably as soon as the power was switched on?

A. Probably because your transmitter was not set up correctly. (See Sections 5 - 8 of the manual for the set-up procedure.) The two commonest causes are: 1. The transmitter is set to PCM mode. (Set it to PPM mode.) 2. The servo reversing switches on the transmitter are set wrongly. (Set them correctly according to the manual.) Be sure to hold the Hoverfly by the rotor hub during initial power-up to prevent it taking off unexpectedly. See picture, right.

Q. What are the benefits of using genuine Snelflight propellers?

A. Our propellers have been carefully designed for optimum thrust and accurate balance. The propellers in each set have also been precisely matched to give smooth flight. Propellers from other manufacturers may give poor thrust, high levels of vibration (which can harm the Hoverfly) and unsteady flight.

Q Why does the Hoverfly tend to skitter off sideways when I try to take off?

A. There are several reasons for this. Firstly the above 90º offset makes the Hoverfly confusing to trim while on the ground. To trim correctly, centre all the transmitter trims (including sub-trim settings on computer transmitters). Next, trim the ECP as described in the manual (section 8). The Hoverfly will now be trimmed well enough to take off. The second problem is ground effect. Because the Hoverfly is so small it behaves differently from larger models when close to the ground. To achieve a safe take-off it is important to get out of ground effect quickly. To do this, advance the Collective (throttle) to just below take-off power and allow time for the rotor to get up to speed. Then give a decisive burst of Collective in order to hop about 30 cm into the air.
Finally, if the Hoverfly topples whilst revving up it is probably because it is not standing upright. Correct this by adjusting the undercarriage wires. The wide-base training undercarriage (see above) helps a lot to prevent toppling at take-off and achieve a vertical ascent.

Q. What is the difference between the Hoverfly and a computer simulator?

A. The Hoverfly is an authentic three-dimensional miniature trainer for 30 size model helicopters, and is far more realistic than a flat screen representation could ever be. Because it is real, the pilot feels a similar adrenaline buzz to that felt when flying an outdoor model. This helps the pilot learn to prevent panic reactions in difficult situations: a leading cause of crashes.

Q. Why fly model helicopters?

A. In short, flying model helicopters is great fun! You get to control a little machine which has complete three-dimensional freedom, and make it move in very precise ways. You can swoop and dive, loop and roll, and achieve tremendous speeds. You can hover over a spot and carry out pretend airlift rescues, or any number of other fantasies.

Flight has a magical, even spiritual quality to it, and making it happen yourself feels very special and relaxing. Learning to fly model helicopters also helps with learning the real thing, in my limited experience!

Q. Why choose the Hoverfly?

A. Learning to fly a model helicopter is not particularly easy. You have to acquire a new sense of balance, letting the aircraft become an extension of yourself. In this respect it is a little like learning to ride a bicycle. To do it at all well, it has to become totally natural for you, without involving conscious thought.

Once learned, either skill becomes very hard to describe to someone else; it is as if you have gained a new sense within your body which other people do not yet have. You can't forget it once you have it. You can't imagine how it's possible until you do!

A bicycle is controlled using the whole body, responding to motion changes detected by a number of the senses simultaneously. A model helicopter, on the other hand, is controlled purely by small movements of the fingers, with feedback coming only through the eyes. Whereas a bicycle can really only fall over sideways, a helicopter can fall over in any direction, and because you are not inside, it can turn to face you, so that your left becomes the helicopter's right, and so on! These factors make helicopters quite challenging to learn, and you will be grateful for all the help you can get.

The Hoverfly is not especially easy to fly compared to other models. This is important, since it is supposed to be a realistic trainer. It's not particularly difficult either. However, it makes the process of learning easier in two major ways.

First of all, the Hoverfly comes ready to fly, which means that you can be confident that it is at least capable of flight when you first take the controls. You have to construct most models yourself, so they do not afford this luxury because there are so many fine details which have to be set right.

To set up a helicopter for flight, you have to be able to fly it, but to learn to fly, you need a helicopter that is properly set up. This catch frustrates many who try, and the only sure solution is to enlist the help of someone who can already do it.

Secondly, the Hoverfly operates indoors, and is amazingly straightforward. You do not have to worry about the weather, finding a field, different grades of fuel and glo-plugs, getting engines to start, keeping numerous batteries charged, and so on. There are no servos, linkages, ball joints, or swash plate. There are no receiver, no battery pack, and no frequencies to worry about. There are hardly any adjustments at all. You just plug it in, and after a few minutes spent initially to configure the Hoverfly to your particular controller, you are ready to go.

It will fly continuously without recharging. You can cover the floor with quilts to crash onto, and if it does break, the spares cost a fraction of the outdoor model equivalents. The cost of crashing an outdoor model can easily exceed £100, whereas you can buy a whole new Hoverfly (excluding the rest of the kit, such as the mains adapter) for £99.95! The majority of individual parts cost just a pound or two.

If you are serious about learning, you should bear in mind that you will get through a few parts, especially thrust propellers, which are the commonest casualties. Lay in a stash of these (a pack of five costs only £7.90). It isn't really worth buying any other parts ahead of time, because it is entirely random as to what else will get broken. You may well get away with little or nothing.

You will need a certain degree of practical ability, because the Hoverfly is designed to pop apart in a crash, (which saves things from breaking). You need to be able to get it assembled again, and check that the mechanics run properly. It is mechanically very simple, and does not explode into a million bits in a crash, but the major sub-units (such as the tail) do come dislodged during impacts.

If you feel comfortable carrying out repairs such as replacing bicycle brake blocks, using simple tools and making small adjustments so that things work right, then you will have no major difficulties with the Hoverfly. The manual is very helpful.

There are simulators available which let you fly on a computer, and these can help you learn. However, a lot of crashes are caused by bad panic reactions, and on a simulator you just don't get up a realistic level of adrenaline. In addition, simulators simply don't give you the wonderful feeling of watching a real-life machine overcome gravity and rise into the air. This is what flying is all about!

There are, of course, a number of other small indoor model helicopters. However, battery operation tends to give very short flight times between half-hour re-charges. In addition, they generally have rotors with fixed-pitch blades. This means that in order to increase overall lift to ascend, it is necessary to speed up the entire rotor. This takes time to do, making the machine slow to respond, more difficult to fly and quite unlike an outdoor model. The Hoverfly can respond immediately to a demand for increased lift, making it far more representative of larger helicopters.
 

Q. What do I need to know before beginning to Fly

A. Having bought a Hoverfly and configured it to your controller as described in the manual, the following seems to be a good way to start learning to fly.

Choose a room with as much space as possible. Eight feet square is a reasonable minimum. Try to move any furniture as far back as you can. Next, spread out the largest quilt or duvet that you have available, to create a soft surface to crash onto. If you have more quilts, these can be used to cover up air traffic hazards such as brick fireplaces or bulky furnishings.

Place the Hoverfly in the middle of the quilt, making sure that it is standing upright and facing away from you. If you haven't done so, it isn't a bad idea to fit the training undercarriage, since this makes taking off vertically quite a bit easier for beginners. Run the command line to the edge of the quilt, and find a position that is comfortable for you. Switch everything on, and you're ready to go. If you are new to aircraft, you should by now have studied the diagram in the manual which shows what the various controls do. It's important to know!

Rev-up the Hoverfly by slowly advancing the throttle, and be ready to shut it down if it starts to topple over. This will happen if it is not standing vertically on the soft quilt. When it is revved-up and beginning to seem light on its skids, it is ready for take-off. At this point, it is important to give it a slight burst of throttle in order to get airborne quickly. You cannot learn to fly until the aircraft is in the air! If you hesitate too much, the Hoverfly will bounce about until it topples over, or else skitter off at high speed until it bumps into something.

Almost as soon as the Hoverfly is airborne, you will have to back off a little on the throttle to prevent it from rising too far. A height of between one and two feet is perfect, because crashes onto the quilt from this height will do no damage. It will take quite a few goes to get this right, since reducing the throttle too much will cause the Hoverfly to sink back to the ground again.

After each landing, check the Hoverfly over to make sure nothing is loose, then place it back in the middle of the quilt before trying again. This gets to be a bit of a chore, and it will be tempting to take off from wherever the Hoverfly has come to rest if it is still upright. However, you will be closer to hazardous obstacles if you do; I learned this the hard way. Always put the thing back in the middle!

Once in the air, you are going to have to work the cyclic controls to guide the Hoverfly around. It will drift off in one direction or another, and you have to move the control stick the opposite way to compensate. Centring the stick will not make the aircraft stop and hover! You have to actively arrest movement by applying just the right amount of opposite control. Too much, or for too long, and the Hoverfly will fly off the other way.

It is important to understand that the Hoverfly moves in the direction in which it is tilted. In order to fly it, you have to learn to notice slight disturbances in tilt, before they result in movement. This allows you to correct them instantly, to keep the aircraft still. If you wait until the Hoverfly is moving before applying correction, it will invariably be too late.

Learning cyclic control will take a number of attempts. However, because you are flying over the quilt, you can cut the throttle and drop to the ground as soon as the Hoverfly gets close to the edge of the flying area. Provided that it is not too high it will be undamaged by this, and you can keep trying again until you begin to get a feel for it.

Before long, flights will last for quite a few seconds (this is actually a long time!), and at this point you will need to begin steering it in the horizontal plane. While learning to fly, you will want to keep the Hoverfly facing away from you, so that the controls are 'the right way round'. If it starts to nose around a bit, you have to use the rudder control to steer it back again. Fortunately, the Hoverfly's gyro is very powerful, so that the aircraft tends to stay pointing in one direction for quite a long time before it drifts.

Q. What Type of Controller Do I Need?
by Phillip Jermyn, Technical Director, Snelflight Ltd

A. To operate the Hoverfly, you will need a control handset (transmitter). The Hoverfly TXI package (H301CF) includes our mini-controller called the FlightPad, which has been specially designed for the Hoverfly. However the Hoverfly II package (H201CF) does not include a controller; you have to provide your own. The controller needs at least four channels with servo reverse switches, plus a trainer (buddy box) socket. There are a lot on the market which have these facilities, and the Hoverfly can be configured to work with just about any of them. However, when choosing, you might want to bear in mind the following:

On the whole, the simple four-channel controllers are a lot easier to use with the Hoverfly than the fancy multi-channel computer types, especially if you are a beginner. This is because computer radios have literally dozens of set-ups and controls, many of which have to be set correctly in order to work the Hoverfly. It is true that in general, the various facilities have to be switched off, but actually doing this involves working through a long sequence of 'menu' type button selections whilst trying to follow the instruction manual. You simply don't need this sort of hassle and uncertainty when you are new to the hobby, and don't know what any of the jargon means.

The simple controllers are also the least expensive. Rock bottom on price is the Futaba Skysport 4, which usually comes as part of a set along with a receiver, servos, battery packs and so on. You don't need most of the other stuff (although you do need the radio's battery pack and charger), so it's well worth asking nicely to see if the dealer will split the set. Quite a few will, and some will have a spare radio or two left over from sets previously split up for the other bits. It's worth ringing around.

We recommend the Skysport 4 because it has only the features required by the Hoverfly and no more. The Hoverfly comes factory preset for Futaba radios, so there will be very little left for you to set up. If you do buy a Skysport 4, it will work much better if you take the trouble to open it up and remove the mechanical limiter fitted to the throttle joystick mechanism. This plastic widget prevents the throttle stick from moving as far forwards (or backwards) as the other stick, greatly reducing Hoverfly climbout performance. If you compare how far the two sticks move, the difference will be obvious. No one seems to know what this limiter is for (many other radios have it too), but it can be easily removed as follows:

1) Open the battery compartment and remove the battery pack, disconnecting its lead from the radio.
2) Release the four screws on the rear of the radio, and remove the back cover (this is safe, and fully sanctioned by Futaba, who describe the procedure in their instruction booklet). Take care not to touch the electronics with your screwdriver.
3) Unscrew and remove the throttle stick friction spring. This spring is a strip of metal, located far right as you look at the inside of the radio from the rear.
4) Having removed the spring, you can now get to the screws which attach the plastic throttle limiter widget to the stick mechanism. Remove the screws and the plastic widget itself, then replace the friction spring if you want the throttle to have a 'notched' feel. Most helicopter pilots don't, by the way, because the notches make it harder to hover.
5) If you want to, you can adjust the stick self-centre spring tensions at this time. This is done by turning the small screws found next to the centring springs in the corners of the stick mechanisms. The Futaba instruction manual has a diagram.
6) Replace the back cover, making sure that the training socket and battery lead locate properly.
7) Replace the battery pack and close the compartment.

Please note that the Skysport 6YG is not well suited to the Hoverfly, even though it doesn't have the above mechanical throttle limiter. This is because it has been designed electronically to give reduced throttle signal range, just as if it did have a mechanical limiter fitted. An electronic modification is therefore needed to increase the throttle range. I can supply details to anyone wishing to try this (a single resistor value needs to be changed); however I doubt that Futaba would sanction it! The Skysport 6 is attractive because it has adjustable rates on the other controls, but I would recommend avoiding it because of the above problem. The Hitec Focus 4 is an inexpensive and superb radio that also has adjustable rates, and works brilliantly with the Hoverfly.

The downside to buying a cheap radio is that you can't use it to fly an outdoor model helicopter later on. For this you need at least five channels, plus a bunch of other features that you only get on 'heli' radios. However, using an expensive radio to learn on seems a waste to me, since you end up with worn-out joysticks by the time you can fly. I think it's worth buying a cheap one first, and then getting a fancy heli radio when you are sure you like the hobby.
 

Q. What about the Umbilical?
by Phillip Jermyn, Technical Director, Snelflight Ltd

A. The Hoverfly operates at all times on a thin umbilical, called the Command Line. The downside to this is obvious; however, the command line is thin (0.7mm) and unobtrusive, and has several major advantages.

Firstly, you can fly continuously, which is great for learning. More generally, direct mains power means that there is almost no preparation required before a session, so if you have a spare five minutes, you can spend it flying. Conventional models are not like this; you have transmitter, receiver, glo-starter, engine starter or flight battery packs to charge up and maintain, as well as travel to and from a flying field in order to get a flight.

Secondly, the absence of batteries saves a lot of weight, which makes the Hoverfly much less prone to breaking when it crashes (Hoverfly weighs under 70g). The motors run cool and last a long time, unlike those on standard electric helicopters in which the main drive motor has to work so hard it seems ready to melt. Also, you are saved the cost of several flight packs and a fast charger.

The Command Line supplied as standard is 3.5m (about 12 ft) in length. This lets you reach the corners of a fairly large room. A 6m (20 ft) upgrade line is available if needed. Despite being so thin, the wire is amazingly robust. As spares, we have sold very few indeed.

Outside, the umbilical is somewhat restrictive (the sky is just so big!); however, the Hoverfly is not intended to fly outdoors, since it is too light to cope with more than the slightest wind, and too small to see from any distance. Because the Hoverfly is never more than a few feet away from you, we have avoided radio communication entirely. The transmitter connects to the Hoverfly's control system by means of the buddy box socket instead. This method extends the transmitter's battery life greatly, and eliminates worries about frequencies and interference.
 

Q. Why does my Hoverfly Flight Wobble ?
by Phillip Jermyn, Technical Director, Snelflight Ltd

A. When everything is working properly, the Hoverfly will fly smoothly. At its best it is silky, with a magically graceful quality. This level of performance frequently remains even after multiple crashes, but if your Hoverfly is more reminiscent of a concrete mixer, then this article is for you!

Wobble in flight can physically be caused only by something that's rotating. This is useful, because it narrows the search down to the rotor, and the parts thereon. There are several types of wobble.

1) Mass imbalance: This means, quite simply, that the centre of gravity of the rotor is not in the middle, so that a net centrifugal force rotates with the rotor as it spins, pulling the helicopter as it goes. It can be caused by differing component weights (particularly the wooden arms, which vary one from another). This effect is very small, however. Alternatively, if the rotor arms are not equally spaced 120 degrees apart, then the rotor will be out of balance. The wooden arms can occasionally get bent out of shape in a crash; alternatively, the arms may finish up out of position if the rotor is repaired. The carbon fibre rotor is very resistant to physical distortions.

2) Thrust imbalance: This means that the three motors are not providing equal thrust. This is the commonest cause of wobble, with several sub-causes:

The propellers need to be matched for thrust, since they differ from one another in spite of coming from the same mould, because they distort randomly during cooling. At Snelflight, we measure the thrust of each one on a special machine. They are then grouped for thrust into numbered bins, hence the grading number on the pack. The idea is that any three props from the same bin are close enough to work together without wobble. The actual differences are small, so that props of any grade will give almost identical climbout performance, but mismatched props are a leading cause of wobble, because matching has to be so precise. The props are stable, so they don't change thrust in normal use, though chips and other damage can affect them.

Propellers which are themselves out-of-balance (they vibrate in use) will generally perform less well than well-balanced ones. They also stress the rotor, especially where the motor bracket is glued to the arm. Snelflight propellers have been designed for precise balance, whereas those from other manufacturers may not have been.

Thrust imbalance can also be caused by a faulty motor (rare) and by a poor electrical connection to a motor. The latter can be caused by the vibration from running out-of-balance propellers, which can break the solder connections after a while. Check that the wires are solidly soldered to the motor tags. Check too that the motors all turn freely. It is possible to dislodge the lower motor bearing while fitting a propeller, if the armature isn't held firmly enough. This will cause stiffness. Unfortunately, the plastic housing that holds the bearing often gets cracked in the process, so that the bearing will no longer stay in place. This calls for a new motor, or a very careful cyano repair.

The motors stay well matched during their working life, but their brushes and commutators do eventually wear out. They typically last a few tens of hours, and all three tend to wear out at the same time. Black residue can often be seen inside the translucent backplate as a motor gets towards the end of its life. At about this time, a motor will sometimes begin to run poorly, producing low or inconsistent power output. This will cause a wobble. Typically, one motor will give reduced thrust compared with the others, but at a certain throttle speed (roughly the hover setting), the motor will suddenly notch up to full power. If you hold the helicopter by the rotor and slowly bring up the throttle, you can hear (and feel) this effect, and it is pretty easy to identify the particular motor this way. A hard knock will often trigger this fault if it is about ready to happen anyway, so it may appear after a crash. Unfortunately, there is no cure except a replacement motor.

3) Mis-aligned motors: If the motors are not all set at the same angle, then wobble will be created. In particular, all three motors should have roughly zero radial slant. If they seem to be sloping slightly inwards or outwards this doesn't matter provided that they are all the same, but if one is very different, this creates a net radial force which turns with the rotor, causing wobble.

4) Bearing hole not vertical: This will cause a wobble, because the rotor disc will turn on its axis, in spite of the fact that the bearing hole does not lie along it. If the hole is slanted, then it will follow a conical path, dragging the mainshaft and fuselage with it. This can only really be caused by faulty manufacture, or inaccurate crash repair. The former is unlikely, since the rotors are assembled on a jig, and if one were bad in this way, they would all have to be. Please note that if the main shaft itself is bent off the vertical then the helicopter will fly smoothly, but the fuselage will be slanted during flight. This is because the shaft is fixed, and the rotor turns around it.

5) Bad carbon brush contact: This can cause wobble, since a motor will not provide full thrust if it is not getting proper uninterrupted power. The wobble often occurs during rapid climbout, even though the aircraft is smooth at hover. The three brushes under the rotor are the issue, since the upper brush is common to all three motors and hence affects all three in unison. There is one lower brush for each motor, and they all have to make good contact all the way around the commutator. Imperfections generally disappear as the brushes 'bed-in' during the first couple of minutes of flight following a rebuild.

A Hoverfly that is out-of-balance or that has mismatched propellers will be quite flyable, the wobble being merely a cosmetic intrusion. If the wobble is so bad that it makes flying difficult, then there is almost certainly something else wrong, such as a faulty motor, or loose wiring. Cosmetic wobbles respond well to Blu-Tack balancing (see manual). Switching the propellers around can also help, especially if any of them is at all damaged since this alters the effect of any small differences in thrust, sometimes to considerable advantage. When adding Blu-Tack, bear in mind that you are correcting for a mixture of the above types of wobble. For smooth flight, the rotor may not need to be perfectly balanced in weight terms. The way in which the different wobble types interact is quite complex, and interestingly enough, can lead to a composite wobble at various multiples or fractions of the rotor's speed. With experience, this can give you some clues about what corrections to make.

Q. Why does my Hoverfly have such poor Climbout?
by Phillip Jermyn, Technical Director, Snelflight Ltd

A. When operating properly, the Hoverfly hovers at about 65-70% throttle and has rapid climbout. Its performance matches or even exceeds that of outdoor model helicopters in relation to its size. If your Hoverfly barely seems to get off the ground then please read on. There are a number of possible causes for poor climbout, but the problem is almost always quite straightforward to fix.

An important difference between the Hoverfly and outdoor model helicopters is that the Hoverfly has no mechanical throttle linkages to adjust. While this does simplify things, it also means that climbout performance is totally dependent upon the transmitter's throttle signal range, because it is not possible for example, to compensate for limited servo travel by using a longer crank lever. In order perform at its best the Hoverfly needs to receive a throttle signal with full 100% travel, and unfortunately there are lots of possible reasons why a transmitter might not provide this. Almost all Hoverfly climbout problems are caused by insufficient transmitter throttle travel; quite simply this means that when the throttle stick is at maximum, the transmitter is sending a signal to the Hoverfly which is below maximum, resulting in less-than-maximum performance!

Helicopter radios generally have several controls and adjustments which affect throttle travel, and it obviously makes sense to check these first. The main ones are described below in some detail, since a general understanding of what the controls do will help in finding optimum settings.

Transmitter Throttle Adjustments

1) Travel Adjusts (ATVs, Endpoint Adjustments): These controls set the full-stick output signal levels, and there are usually two settings per channel, so that the signal level at each end of the stick's travel can be set independently. Setting the ATVs asymmetrically does not change the signal at mid-stick. How the throttle ATVs should best be set depends on a number of factors as we shall see. However, they should certainly not be set below +/-100%, and an increase at the top end will generally improve climbout performance.

2) Throttle Curve: This adjustment allows you to control the relationship between stick position and channel output, to a degree of precision which varies from radio to radio. This relationship is best expressed as a graph or 'curve', with channel output plotted vertically against stick position on the horizontal axis. Some radios let you see this graph on a liquid crystal display, and all let you set a number of points on the curve, which the computer then connects with (usually) straight lines. As a minimum, you can set the two stick endpoint levels (this is like setting the ATVs), plus one point in between. Modern radios usually let you set more points than this, and also allow you to set several complete curves, which can be selected with a switch during a flight session. For instance you might have a curve suited to hovering practice, another for flying about, and another for aerobatics involving inverted flight. The latter would probably be a 'V' shaped curve with minimum throttle at centre-stick. The throttle curve is one of a number of settings used by model helicopter pilots in order to optimise climbout performance on their machines. To make a helicopter climb it is necessary to combine an increase in collective rotor blade pitch with an increase in engine throttle. Ideally the two are balanced so that the rotor speed remains constant at all times, i.e. engine throttle is increased to exactly compensate for the extra loading when the collective pitch is increased, etc. The Hoverfly has no collective pitch control, and climbout depends wholly on throttle. This simplifies things greatly, but the throttle curve nevertheless needs to be set appropriately. It should be adjusted to provide a proportional (straight line) relationship between joystick and output signal, travelling from -100% to +100% with the zero point at mid-stick. The relationship between the throttle curve endpoints and the ATVs depends on the transmitter. Sometimes the ATVs over-ride the throttle curve settings (never the other way around, as far as I know), sometimes the lowest of the two settings prevails, and sometimes one setting is scaled by the other. Setting both to +/-100% is a good way to start since it covers all these eventualities.

3) Trims (and electronic sub-trims): Trims are the small adjuster levers next to the joysticks; they allow the mid-stick signal levels to be adjusted so that the aircraft's control surfaces are at their neutral positions when the joysticks are centred. There is a trim for the throttle, and it should generally be centred with the Hoverfly. On many transmitters, particularly cheap ones, the trim simply shifts the whole stick range up and down; changing the trim therefore alters both endpoints as well as the signal at mid-stick. On other types the trim adjusts the mid-stick signal without changing the endpoints. Transmitter manuals seldom give this sort of subtle detail, but it can be useful to know, and it's well worth experimenting. If the trim alters the endpoints then pushing it forwards will improve Hoverfly climbout! Many transmitters also have electronic sub-trims which can be adjusted along with all the other computerised settings. The throttle sub-trim should generally be centred, since zero output at mid-stick is desirable and sub-trims never alter the endpoints.

Cheap radios often do not have any of these controls, except for external trims. However there are other causes (and solutions!) for Hoverfly climbout problems; please read on.

Mechanical Throttle Limiters

Many transmitters have mechanical stops on the throttle stick which limit physical movement to less than the full range. It is easy to tell whether your transmitter has these stops, by comparing the physical positions of the left and right joysticks when pushed fully forwards (or backwards). The stops typically reduce throttle range by about 20%, with a disastrous effect on Hoverfly climbout! I have a theory as to why these stops are fitted (see below), but in practice they seem to be nothing but a nuisance. The good news is that they can almost always be removed easily.

The stops usually take the form of one or more plastic components screwed to part of the throttle joystick gimbal. By carefully comparing the two joystick mechanisms they can be spotted easily enough. They generally comprise either a pair of wedge shaped pieces of plastic (one for each end of the stick travel), or a single 'widget' which limits stick range at both ends. Because they are screwed into place they can be restored later (if you want them back for some bizarre reason). Transmitter manuals typically sanction (and describe) opening up the unit to make various adjustments, so no warranty problems arise from delving inside.

Computer radios frequently have throttle limiters fitted, and on these units the ATVs can be set to +/-120% or so to compensate for the reduced stick throw, as an alternative to removing the mechanical stops. However it is better to remove them, since throttle precision is impaired by compressing the full range into diminished physical stick movement.

Certain transmitters, specifically the Futaba Skysport 6YG, do not have mechanical throttle limiters, but instead have their electronics rigged up to generate a throttle signal range just as if limiters were fitted. Thus the throttle has about 20% less signal range than the other channels, but there are no plastic 'widgets' to remove! An electrical modification is required to solve this one (a single resistor value needs changed in the Skysport 6); I can supply details of this on request. However if a transmitter is to be purchased especially for the Hoverfly, I would strongly recommend avoiding the above type. The Skysport 4 is a good choice for the Hoverfly (and cheaper than the Skysport 6). It does have mechanical stops, but these are of the 'single widget' type and are easily removed.

Why Fit Throttle Limiters?
On the face of it, throttle limiters seem crazy. Even after much consideration, they still seem crazy. They make the transmitter awkward to use with the Hoverfly (and other electric models), and reduce throttle resolution on all models by squeezing the throttle range into less than full joystick movement. The only semi-explanation I have been able to come up with is that the limiters force the modeller to rig up the model's throttle mechanics (cranks and pushrods) to use only the central part of the servo's angular range. The linear displacement of a pushrod is roughly proportional to the sine of the crank's angular motion; pushrod movement is therefore a fairly linear function of servo rotation in the centre region, say between +/-45º. Outside this range pushrod motion falls off rapidly, dropping to zero at the crank dead centre positions. A precise relationship between joystick position and engine throttle setting is crucial on many models, especially helicopters, so proportional actuation mechanics are helpful. However a typical engine throttle lever is itself a crank, so the non-linearities at opposite ends of the pushrod will cancel one another out to some degree. Also, it seems odd to single out the throttle in this way since linearity issues apply to the other aircraft controls as well, especially helicopter collective pitch which has to track throttle according to a precise relationship. It is perhaps surprising that linear output servos with rack-and-pinion mechanisms are not more popular, since they would eliminate the linearity issue. They used to be made, but I haven't seen them recently. I find it frustrating that transmitter manufacturers force their views on us, instead of supplying the flexibility we need in order to find solutions which suits us.

Signalling Standards

This is where I really get down to business; the foreplay's over! Radio control transmitters send information about the positions of all the channels by means of a series of timed electrical pulses. One pulse is transmitted for each channel in turn; the setting of a channel is denoted by the time elapsed between its pulse and the previous one. The whole sequence repeats about 50 times per second, thereby updating the channel positions continuously (strictly speaking, only PPM transmitters work this way. However, even PCM signals get converted to timed pulses inside the receiver before reaching the servos).

Although all transmitters work this way, there is unfortunately no universal agreement over the scaling of this scheme. On a JR transmitter, a centred channel is represented by a time period of 1.50 ms. On a Futaba transmitter, the time is 1.52 ms. This difference is minor, amounting to about 5%, so it doesn't prevent JR servos being used with a Futaba radio, for instance. However, owners of JR radios will notice that the Hoverfly comes out of the box slightly out of trim, because it is factory preset for Futaba.

A far more important issue is that of channel range, since this affects Hoverfly climbout. In the past, 100% stick deflection either side of centre was denoted by a timing change of 0.5ms; the time period representing a channel could therefore vary between about 1.0ms and 2.0ms. The Hoverfly controls (including the throttle) were designed to match this. However, during the last few years the R/C industry has been gradually adopting a new standard of +/-0.4 ms to represent 100% deflection. Channel range has effectively been reduced by 20%, without any acknowledgement being made anywhere, as far as I know. The reduction has gone even further on some transmitters. I mentioned the Futaba Skysort 6YG earlier in relation to throttle limiters; the 'electronic limiters' built into it actually reduce throttle throw to +/-0.3ms (not much over half of +/-0.5 ms throw), so it's hardly surprising that it doesn't work very well with the Hoverfly. Futaba's FF9 transmitter has +/-0.3 ms signalling on the first four channels (the joysticks). However, it does have ATVs, so the throttle can be set above 100% to compensate. I suggest +/-150%, or whatever the maximum is!

I'm not sure which manufacturer led the way with these changes, but most seem to have followed suit now. Hitec haven't as yet, and their Focus 4 transmitter is a superb (and inexpensive) radio that works brilliantly with the Hoverfly.

In March 2002 we modified the Hoverfly electronics to match the new +/-0.4 ms standard. We have been in a dilemma over this, because changing too soon would result in a lot of Hoverflies being over-driven by the older +/-0.5 ms radios, with possible complications. We didn't want to change over too soon. The result of the change is that the Hoverfly now works properly on most current radios, although it is still well worth removing the throttle limiters.

If you are experiencing climbout problems with a Hoverfly dating from before the changeover (or even if you are not sure about it), please get in touch with us. We will happily modify an older control unit (ECP) to the new standard free of charge.

An Afterword

The Hoverfly is supposed to fly really well! When it is working properly, very few pilots are unimpressed by its performance. Please get in touch with us if you are unhappy with it in any way; we are always happy to help.

 

Q. How is the Hover Fly assembled?

A. All Hoverfly airframe assembly is done by hand, with meticulous attention to quality at all stages. Many key components are tested several times during the assembly process.

Every finished Hoverfly is then individually test flown and balanced for smooth flight where necessary, just prior to packing. This is why you will sometimes see a small weight made from special black putty, attached to the rotor next to one or more of the motors.

Materials have been very carefully selected to optimise weight, strength and reliability, with no less than nine different plastics being used. When we recently found that a component was prone to wear, it was re-designed using a new material, and exhaustively tested. This eliminated the problem completely.

The Electrocyclic Control Processor circuit boards are assembled using the very latest in automated component placement robotics. Parts are positioned and automatically checked at a rate of over 20,000 per hour! Finished boards are then re-checked for correct operation on a special test rig.
 

 Products > Hover Fly > FAQ